If you go portable garage I would suggest in having filted positive air flow through it. not some thing like a tornado, but just something to move the air out while moving filered air in.
When there is going to be frost out side (low humitity), heat the incoming air a little, then stop heat for a while, then stop the air and close the garage off (sealed). This will ensure that the there will be minimal amoint of dust as well as humitiy.
Global warming is weird. East coast winters are way worse than Alaskan winters now adays.